In a conventional tripod-connecting adapter for connecting a pair of binoculars to a tripod, there has been proposed a one including an adapter body on which a through hole is formed, a screw member that is rotatably inserted into the through hole and whose tip portion is connected to a mechanical axis (a joint shaft) of the pair of binoculars, and a friction-force-generation member that is disposed on the adapter body and has given friction force upon connecting the screw member to the mechanical axis (see, for example, Japanese Patent Application Laid-Open No. 2002-072104).
When a pair of binoculars is connected to a tripod by using a conventional tripod-connecting adapter, and when a digital camera, which is a heavy load, is connected to an eyepiece portion of the pair of binoculars, the whole of the binoculars tilts from a horizontal position around the joint shaft or an interpupillary distance of the binoculars varies by the weight of the digital camera or pressure upon releasing the digital camera.